With the rapid evolution of the wireless communication technique and increasing requirements for traffic throughput, a new type of network architecture, also known as an Ultra-Dense Network (“UDN”), has been proposed. The UDN is predominantly expected to be deployed in a form of “coverage islands” serving relatively small areas (e.g., an office building, a shopping mall, etc.). In general, a particular area is expected to be served by one UDN only, i.e., although possible, parallel deployments of multiple UDNs are considered unlikely. Adjacent or spatially separated UDN deployments are expected to be relatively well-isolated due to large radio propagation losses. This may be due to the fact that UDNs are expected to operate on high frequencies, e.g., in 10-100 GHz. It is therefore generally desirable to enable UDNs to utilize the full available bandwidth in a given frequency band in order to maximize the peak data rate and capacity, as opposed to the today's dominant practice of partitioning a frequency band in multiple frequency blocks assigned to only one network. For a better understanding of the UDN, the following will describe some operational details in reference to FIG. 1, which schematically illustrates a scenario for inter-UDN co-channel spectrum sharing.
First, it is assumed that there are two UDNs deployed in an open office as shown in FIG. 1, wherein the first UDN comprises an access node (“AN”) 1, an aggregation node (“AGN”) 1 which is a special AN and has a wired connection to a core network, a terminal device (“TD”) 1 and a TD 3 and the second UDN comprises ANs 2 and 3, TDs 2 and 4, and an AGN 2. It is further assumed that the first UDN and the second UDN are owned by different operators. Under this network architecture and deployment, a TD, when moving around within the coverage of a single UDN, can only access to different ANs belonging to the same operator. For example, although the AN 2 is further from the TD 2 than the AN 1, the TD 2 would have to access to the AN 2 rather than the AN 1 due to the same operator. Likewise, the TD 3 would access to the AN 1 rather than the AN 2. In this situation, when the adjacent, neighboring or perhaps partly overlapping UDNs 1 and 2 share the same frequency channel or operate on overlapping frequency channels, it is very likely that interference may arise between the nodes in UDNs 1 and 2, e.g., the interference between the wireless link 1 from the UDN 1 and the wireless link 2 from the UDN 2, as illustrated in FIG. 1. The impact of such inter-network interference on the wireless link quality may not be ignorable and would become more serious when a great number of the TDs are moving across the overlapping area of the different UDNs owned by respectively different operators.